fe-lobj.c

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/*-------------------------------------------------------------------------
 *
 * fe-lobj.c
 *    Front-end large object interface
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/interfaces/libpq/fe-lobj.c
 *
 *-------------------------------------------------------------------------
 */
 
#ifdef WIN32
/*
 *  As unlink/rename are #define'd in port.h (via postgres_fe.h), io.h
 *  must be included first on MS C.  Might as well do it for all WIN32's
 *  here.
 */
#include <io.h>
#endif
 
#include "postgres_fe.h"
 
#ifdef WIN32
#include "win32.h"
#else
#include <unistd.h>
#endif
 
#include <fcntl.h>
#include <limits.h>
#include <sys/stat.h>
 
#include "libpq-fe.h"
#include "libpq-int.h"
#include "libpq/libpq-fs.h"     /* must come after sys/stat.h */
#include "port/pg_bswap.h"
 
#define LO_BUFSIZE        8192
 
static int  lo_initialize(PGconn *conn);
static Oid  lo_import_internal(PGconn *conn, const char *filename, Oid oid);
static pg_int64 lo_hton64(pg_int64 host64);
static pg_int64 lo_ntoh64(pg_int64 net64);
 
/*
 * lo_open
 *    opens an existing large object
 *
 * returns the file descriptor for use in later lo_* calls
 * return -1 upon failure.
 */
int
lo_open(PGconn *conn, Oid lobjId, int mode)
{
    int         fd;
    int         result_len;
    PQArgBlock  argv[2];
    PGresult   *res;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = lobjId;
 
    argv[1].isint = 1;
    argv[1].len = 4;
    argv[1].u.integer = mode;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_open, &fd, &result_len, 1, argv, 2);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return fd;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_close
 *    closes an existing large object
 *
 * returns 0 upon success
 * returns -1 upon failure.
 */
int
lo_close(PGconn *conn, int fd)
{
    PQArgBlock  argv[1];
    PGresult   *res;
    int         retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
    res = PQfn(conn, conn->lobjfuncs->fn_lo_close,
               &retval, &result_len, 1, argv, 1);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_truncate
 *    truncates an existing large object to the given size
 *
 * returns 0 upon success
 * returns -1 upon failure
 */
int
lo_truncate(PGconn *conn, int fd, size_t len)
{
    PQArgBlock  argv[2];
    PGresult   *res;
    int         retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    /* Must check this on-the-fly because it's not there pre-8.3 */
    if (conn->lobjfuncs->fn_lo_truncate == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_truncate");
        return -1;
    }
 
    /*
     * Long ago, somebody thought it'd be a good idea to declare this function
     * as taking size_t ... but the underlying backend function only accepts a
     * signed int32 length.  So throw error if the given value overflows
     * int32.  (A possible alternative is to automatically redirect the call
     * to lo_truncate64; but if the caller wanted to rely on that backend
     * function being available, he could have called lo_truncate64 for
     * himself.)
     */
    if (len > (size_t) INT_MAX)
    {
        libpq_append_conn_error(conn, "argument of lo_truncate exceeds integer range");
        return -1;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    argv[1].isint = 1;
    argv[1].len = 4;
    argv[1].u.integer = (int) len;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_truncate,
               &retval, &result_len, 1, argv, 2);
 
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_truncate64
 *    truncates an existing large object to the given size
 *
 * returns 0 upon success
 * returns -1 upon failure
 */
int
lo_truncate64(PGconn *conn, int fd, pg_int64 len)
{
    PQArgBlock  argv[2];
    PGresult   *res;
    int         retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    if (conn->lobjfuncs->fn_lo_truncate64 == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_truncate64");
        return -1;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    len = lo_hton64(len);
    argv[1].isint = 0;
    argv[1].len = 8;
    argv[1].u.ptr = (int *) &len;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_truncate64,
               &retval, &result_len, 1, argv, 2);
 
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_read
 *    read len bytes of the large object into buf
 *
 * returns the number of bytes read, or -1 on failure.
 * the CALLER must have allocated enough space to hold the result returned
 */
 
int
lo_read(PGconn *conn, int fd, char *buf, size_t len)
{
    PQArgBlock  argv[2];
    PGresult   *res;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    /*
     * Long ago, somebody thought it'd be a good idea to declare this function
     * as taking size_t ... but the underlying backend function only accepts a
     * signed int32 length.  So throw error if the given value overflows
     * int32.
     */
    if (len > (size_t) INT_MAX)
    {
        libpq_append_conn_error(conn, "argument of lo_read exceeds integer range");
        return -1;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    argv[1].isint = 1;
    argv[1].len = 4;
    argv[1].u.integer = (int) len;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_read,
               (void *) buf, &result_len, 0, argv, 2);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return result_len;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_write
 *    write len bytes of buf into the large object fd
 *
 * returns the number of bytes written, or -1 on failure.
 */
int
lo_write(PGconn *conn, int fd, const char *buf, size_t len)
{
    PQArgBlock  argv[2];
    PGresult   *res;
    int         result_len;
    int         retval;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    /*
     * Long ago, somebody thought it'd be a good idea to declare this function
     * as taking size_t ... but the underlying backend function only accepts a
     * signed int32 length.  So throw error if the given value overflows
     * int32.
     */
    if (len > (size_t) INT_MAX)
    {
        libpq_append_conn_error(conn, "argument of lo_write exceeds integer range");
        return -1;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    argv[1].isint = 0;
    argv[1].len = (int) len;
    argv[1].u.ptr = (int *) unconstify(char *, buf);
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_write,
               &retval, &result_len, 1, argv, 2);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_lseek
 *    change the current read or write location on a large object
 */
int
lo_lseek(PGconn *conn, int fd, int offset, int whence)
{
    PQArgBlock  argv[3];
    PGresult   *res;
    int         retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    argv[1].isint = 1;
    argv[1].len = 4;
    argv[1].u.integer = offset;
 
    argv[2].isint = 1;
    argv[2].len = 4;
    argv[2].u.integer = whence;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_lseek,
               &retval, &result_len, 1, argv, 3);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_lseek64
 *    change the current read or write location on a large object
 */
pg_int64
lo_lseek64(PGconn *conn, int fd, pg_int64 offset, int whence)
{
    PQArgBlock  argv[3];
    PGresult   *res;
    pg_int64    retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    if (conn->lobjfuncs->fn_lo_lseek64 == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_lseek64");
        return -1;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    offset = lo_hton64(offset);
    argv[1].isint = 0;
    argv[1].len = 8;
    argv[1].u.ptr = (int *) &offset;
 
    argv[2].isint = 1;
    argv[2].len = 4;
    argv[2].u.integer = whence;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_lseek64,
               (void *) &retval, &result_len, 0, argv, 3);
    if (PQresultStatus(res) == PGRES_COMMAND_OK && result_len == 8)
    {
        PQclear(res);
        return lo_ntoh64(retval);
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_creat
 *    create a new large object
 * the mode is ignored (once upon a time it had a use)
 *
 * returns the oid of the large object created or
 * InvalidOid upon failure
 */
Oid
lo_creat(PGconn *conn, int mode)
{
    PQArgBlock  argv[1];
    PGresult   *res;
    int         retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return InvalidOid;
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = mode;
    res = PQfn(conn, conn->lobjfuncs->fn_lo_creat,
               &retval, &result_len, 1, argv, 1);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return (Oid) retval;
    }
    else
    {
        PQclear(res);
        return InvalidOid;
    }
}
 
/*
 * lo_create
 *    create a new large object
 * if lobjId isn't InvalidOid, it specifies the OID to (attempt to) create
 *
 * returns the oid of the large object created or
 * InvalidOid upon failure
 */
Oid
lo_create(PGconn *conn, Oid lobjId)
{
    PQArgBlock  argv[1];
    PGresult   *res;
    int         retval;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return InvalidOid;
 
    /* Must check this on-the-fly because it's not there pre-8.1 */
    if (conn->lobjfuncs->fn_lo_create == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_create");
        return InvalidOid;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = lobjId;
    res = PQfn(conn, conn->lobjfuncs->fn_lo_create,
               &retval, &result_len, 1, argv, 1);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return (Oid) retval;
    }
    else
    {
        PQclear(res);
        return InvalidOid;
    }
}
 
 
/*
 * lo_tell
 *    returns the current seek location of the large object
 */
int
lo_tell(PGconn *conn, int fd)
{
    int         retval;
    PQArgBlock  argv[1];
    PGresult   *res;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_tell,
               &retval, &result_len, 1, argv, 1);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_tell64
 *    returns the current seek location of the large object
 */
pg_int64
lo_tell64(PGconn *conn, int fd)
{
    pg_int64    retval;
    PQArgBlock  argv[1];
    PGresult   *res;
    int         result_len;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    if (conn->lobjfuncs->fn_lo_tell64 == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_tell64");
        return -1;
    }
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = fd;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_tell64,
               (void *) &retval, &result_len, 0, argv, 1);
    if (PQresultStatus(res) == PGRES_COMMAND_OK && result_len == 8)
    {
        PQclear(res);
        return lo_ntoh64(retval);
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_unlink
 *    delete a file
 */
 
int
lo_unlink(PGconn *conn, Oid lobjId)
{
    PQArgBlock  argv[1];
    PGresult   *res;
    int         result_len;
    int         retval;
 
    if (lo_initialize(conn) < 0)
        return -1;
 
    argv[0].isint = 1;
    argv[0].len = 4;
    argv[0].u.integer = lobjId;
 
    res = PQfn(conn, conn->lobjfuncs->fn_lo_unlink,
               &retval, &result_len, 1, argv, 1);
    if (PQresultStatus(res) == PGRES_COMMAND_OK)
    {
        PQclear(res);
        return retval;
    }
    else
    {
        PQclear(res);
        return -1;
    }
}
 
/*
 * lo_import -
 *    imports a file as an (inversion) large object.
 *
 * returns the oid of that object upon success,
 * returns InvalidOid upon failure
 */
 
Oid
lo_import(PGconn *conn, const char *filename)
{
    return lo_import_internal(conn, filename, InvalidOid);
}
 
/*
 * lo_import_with_oid -
 *    imports a file as an (inversion) large object.
 *    large object id can be specified.
 *
 * returns the oid of that object upon success,
 * returns InvalidOid upon failure
 */
 
Oid
lo_import_with_oid(PGconn *conn, const char *filename, Oid lobjId)
{
    return lo_import_internal(conn, filename, lobjId);
}
 
static Oid
lo_import_internal(PGconn *conn, const char *filename, Oid oid)
{
    int         fd;
    int         nbytes,
                tmp;
    char        buf[LO_BUFSIZE];
    Oid         lobjOid;
    int         lobj;
    char        sebuf[PG_STRERROR_R_BUFLEN];
 
    if (conn == NULL)
        return InvalidOid;
 
    /* Since this is the beginning of a query cycle, reset the error state */
    pqClearConnErrorState(conn);
 
    /*
     * open the file to be read in
     */
    fd = open(filename, O_RDONLY | PG_BINARY, 0666);
    if (fd < 0)
    {                           /* error */
        libpq_append_conn_error(conn, "could not open file \"%s\": %s",
                                filename, strerror_r(errno, sebuf, sizeof(sebuf)));
        return InvalidOid;
    }
 
    /*
     * create an inversion object
     */
    if (oid == InvalidOid)
        lobjOid = lo_creat(conn, INV_READ | INV_WRITE);
    else
        lobjOid = lo_create(conn, oid);
 
    if (lobjOid == InvalidOid)
    {
        /* we assume lo_create() already set a suitable error message */
        (void) close(fd);
        return InvalidOid;
    }
 
    lobj = lo_open(conn, lobjOid, INV_WRITE);
    if (lobj == -1)
    {
        /* we assume lo_open() already set a suitable error message */
        (void) close(fd);
        return InvalidOid;
    }
 
    /*
     * read in from the file and write to the large object
     */
    while ((nbytes = read(fd, buf, LO_BUFSIZE)) > 0)
    {
        tmp = lo_write(conn, lobj, buf, nbytes);
        if (tmp != nbytes)
        {
            /*
             * If lo_write() failed, we are now in an aborted transaction so
             * there's no need for lo_close(); furthermore, if we tried it
             * we'd overwrite the useful error result with a useless one. So
             * just nail the doors shut and get out of town.
             */
            (void) close(fd);
            return InvalidOid;
        }
    }
 
    if (nbytes < 0)
    {
        /* We must do lo_close before setting the errorMessage */
        int         save_errno = errno;
 
        (void) lo_close(conn, lobj);
        (void) close(fd);
        /* deliberately overwrite any error from lo_close */
        pqClearConnErrorState(conn);
        libpq_append_conn_error(conn, "could not read from file \"%s\": %s",
                                filename,
                                strerror_r(save_errno, sebuf, sizeof(sebuf)));
        return InvalidOid;
    }
 
    (void) close(fd);
 
    if (lo_close(conn, lobj) != 0)
    {
        /* we assume lo_close() already set a suitable error message */
        return InvalidOid;
    }
 
    return lobjOid;
}
 
/*
 * lo_export -
 *    exports an (inversion) large object.
 * returns -1 upon failure, 1 if OK
 */
int
lo_export(PGconn *conn, Oid lobjId, const char *filename)
{
    int         result = 1;
    int         fd;
    int         nbytes,
                tmp;
    char        buf[LO_BUFSIZE];
    int         lobj;
    char        sebuf[PG_STRERROR_R_BUFLEN];
 
    /*
     * open the large object.
     */
    lobj = lo_open(conn, lobjId, INV_READ);
    if (lobj == -1)
    {
        /* we assume lo_open() already set a suitable error message */
        return -1;
    }
 
    /*
     * create the file to be written to
     */
    fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC | PG_BINARY, 0666);
    if (fd < 0)
    {
        /* We must do lo_close before setting the errorMessage */
        int         save_errno = errno;
 
        (void) lo_close(conn, lobj);
        /* deliberately overwrite any error from lo_close */
        pqClearConnErrorState(conn);
        libpq_append_conn_error(conn, "could not open file \"%s\": %s",
                                filename,
                                strerror_r(save_errno, sebuf, sizeof(sebuf)));
        return -1;
    }
 
    /*
     * read in from the large object and write to the file
     */
    while ((nbytes = lo_read(conn, lobj, buf, LO_BUFSIZE)) > 0)
    {
        tmp = write(fd, buf, nbytes);
        if (tmp != nbytes)
        {
            /* We must do lo_close before setting the errorMessage */
            int         save_errno = errno;
 
            (void) lo_close(conn, lobj);
            (void) close(fd);
            /* deliberately overwrite any error from lo_close */
            pqClearConnErrorState(conn);
            libpq_append_conn_error(conn, "could not write to file \"%s\": %s",
                                    filename,
                                    strerror_r(save_errno, sebuf, sizeof(sebuf)));
            return -1;
        }
    }
 
    /*
     * If lo_read() failed, we are now in an aborted transaction so there's no
     * need for lo_close(); furthermore, if we tried it we'd overwrite the
     * useful error result with a useless one. So skip lo_close() if we got a
     * failure result.
     */
    if (nbytes < 0 ||
        lo_close(conn, lobj) != 0)
    {
        /* assume lo_read() or lo_close() left a suitable error message */
        result = -1;
    }
 
    /* if we already failed, don't overwrite that msg with a close error */
    if (close(fd) != 0 && result >= 0)
    {
        libpq_append_conn_error(conn, "could not write to file \"%s\": %s",
                                filename, strerror_r(errno, sebuf, sizeof(sebuf)));
        result = -1;
    }
 
    return result;
}
 
 
/*
 * lo_initialize
 *
 * Initialize for a new large-object operation on an existing connection.
 * Return 0 if OK, -1 on failure.
 *
 * If we haven't previously done so, we collect the function OIDs from
 * pg_proc for all functions that are required for large object operations.
 */
static int
lo_initialize(PGconn *conn)
{
    PGresult   *res;
    PGlobjfuncs *lobjfuncs;
    int         n;
    const char *query;
    const char *fname;
    Oid         foid;
 
    /* Nothing we can do with no connection */
    if (conn == NULL)
        return -1;
 
    /* Since this is the beginning of a query cycle, reset the error state */
    pqClearConnErrorState(conn);
 
    /* Nothing else to do if we already collected info */
    if (conn->lobjfuncs != NULL)
        return 0;
 
    /*
     * Allocate the structure to hold the function OIDs.  We don't store it
     * into the PGconn until it's successfully filled.
     */
    lobjfuncs = (PGlobjfuncs *) malloc(sizeof(PGlobjfuncs));
    if (lobjfuncs == NULL)
    {
        libpq_append_conn_error(conn, "out of memory");
        return -1;
    }
    MemSet((char *) lobjfuncs, 0, sizeof(PGlobjfuncs));
 
    /*
     * Execute the query to get all the functions at once.  (Not all of them
     * may exist in older server versions.)
     */
    query = "select proname, oid from pg_catalog.pg_proc "
        "where proname in ("
        "'lo_open', "
        "'lo_close', "
        "'lo_creat', "
        "'lo_create', "
        "'lo_unlink', "
        "'lo_lseek', "
        "'lo_lseek64', "
        "'lo_tell', "
        "'lo_tell64', "
        "'lo_truncate', "
        "'lo_truncate64', "
        "'loread', "
        "'lowrite') "
        "and pronamespace = (select oid from pg_catalog.pg_namespace "
        "where nspname = 'pg_catalog')";
 
    res = PQexec(conn, query);
    if (res == NULL)
    {
        free(lobjfuncs);
        return -1;
    }
 
    if (res->resultStatus != PGRES_TUPLES_OK)
    {
        free(lobjfuncs);
        PQclear(res);
        libpq_append_conn_error(conn, "query to initialize large object functions did not return data");
        return -1;
    }
 
    /*
     * Examine the result and put the OID's into the struct
     */
    for (n = 0; n < PQntuples(res); n++)
    {
        fname = PQgetvalue(res, n, 0);
        foid = (Oid) atoi(PQgetvalue(res, n, 1));
        if (strcmp(fname, "lo_open") == 0)
            lobjfuncs->fn_lo_open = foid;
        else if (strcmp(fname, "lo_close") == 0)
            lobjfuncs->fn_lo_close = foid;
        else if (strcmp(fname, "lo_creat") == 0)
            lobjfuncs->fn_lo_creat = foid;
        else if (strcmp(fname, "lo_create") == 0)
            lobjfuncs->fn_lo_create = foid;
        else if (strcmp(fname, "lo_unlink") == 0)
            lobjfuncs->fn_lo_unlink = foid;
        else if (strcmp(fname, "lo_lseek") == 0)
            lobjfuncs->fn_lo_lseek = foid;
        else if (strcmp(fname, "lo_lseek64") == 0)
            lobjfuncs->fn_lo_lseek64 = foid;
        else if (strcmp(fname, "lo_tell") == 0)
            lobjfuncs->fn_lo_tell = foid;
        else if (strcmp(fname, "lo_tell64") == 0)
            lobjfuncs->fn_lo_tell64 = foid;
        else if (strcmp(fname, "lo_truncate") == 0)
            lobjfuncs->fn_lo_truncate = foid;
        else if (strcmp(fname, "lo_truncate64") == 0)
            lobjfuncs->fn_lo_truncate64 = foid;
        else if (strcmp(fname, "loread") == 0)
            lobjfuncs->fn_lo_read = foid;
        else if (strcmp(fname, "lowrite") == 0)
            lobjfuncs->fn_lo_write = foid;
    }
 
    PQclear(res);
 
    /*
     * Finally check that we got all required large object interface functions
     * (ones that have been added later than the stone age are instead checked
     * only if used)
     */
    if (lobjfuncs->fn_lo_open == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_open");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_close == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_close");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_creat == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_creat");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_unlink == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_unlink");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_lseek == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_lseek");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_tell == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lo_tell");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_read == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "loread");
        free(lobjfuncs);
        return -1;
    }
    if (lobjfuncs->fn_lo_write == 0)
    {
        libpq_append_conn_error(conn, "cannot determine OID of function %s",
                                "lowrite");
        free(lobjfuncs);
        return -1;
    }
 
    /*
     * Put the structure into the connection control
     */
    conn->lobjfuncs = lobjfuncs;
    return 0;
}
 
/*
 * lo_hton64
 *    converts a 64-bit integer from host byte order to network byte order
 */
static pg_int64
lo_hton64(pg_int64 host64)
{
    union
    {
        pg_int64    i64;
        uint32      i32[2];
    }           swap;
    uint32      t;
 
    /* High order half first, since we're doing MSB-first */
    t = (uint32) (host64 >> 32);
    swap.i32[0] = pg_hton32(t);
 
    /* Now the low order half */
    t = (uint32) host64;
    swap.i32[1] = pg_hton32(t);
 
    return swap.i64;
}
 
/*
 * lo_ntoh64
 *    converts a 64-bit integer from network byte order to host byte order
 */
static pg_int64
lo_ntoh64(pg_int64 net64)
{
    union
    {
        pg_int64    i64;
        uint32      i32[2];
    }           swap;
    pg_int64    result;
 
    swap.i64 = net64;
 
    result = (uint32) pg_ntoh32(swap.i32[0]);
    result <<= 32;
    result |= (uint32) pg_ntoh32(swap.i32[1]);
 
    return result;
}